The Heart and Hyperkalemia
Most of the body’s potassium is located intracellularly. Onl a small fraction (=2%) is found in the extracellular compartment. As serum potassium concentration increases, a decreased ratio of intracellular to exrtracellular K+concentration occurs, and results in a decreased resting cell membrane potential. Increased serum Na+ and Ca+ concentrations limit depolarization of the cell membrane. In addition, there is shortening of the action potential duration from increased membrane permeability to K+. Mild hyperkalemia (6.0mEQ/L), with normal renal function generally needs no treatment. Moderate hyperkalemia (6.0-7.0mEq/L), with normal renal function generally resolves with time and no therapy. Severe hyperkalemia (7.0mEq/L), especially with EKG manifestations, requires immediate therapy. Renal excretion accounts for total maintenance of potassium balance.
Causes of Hyperkalemia
-Transfusion of overaged banked blood
-Renal dysfunction from any cause
-K from cell hemolysis
-K sparing diuretics ( Spironalactone, Triamterene, Amiloride)
-Digitalis in high doses
-Drugs causing tumor lysis
-Low insulin production (DM)
Treatment of Hyperkalemia
- If you get a lab value back that is questionable, be sure to send another sample for a repeat value. In the meantime, alert anesthesia to the possibility of true hyperkalemia, and the necessity for treatment of it.
- Stop all infusions containing K+ (cardioplegic solution, priming solutions, IVs).
- Increase the elimination of K+ from the extracellular fluid:
- Infuse Dextrose and Insulin:
1-2g glucose/kg in children
0.3U R insulin/glucose in children
50g glucose and 15U R insulin in adults
20mg/kg calcium gluconate over 5 min in children
500-1000mg of calcium chloride in adults
- Increase dieresis
- Hemoconcentration on CPB: Hemoconcentrate off as much as pump volume as possible, adding normal saline (for injection) as needed for volume replacement. Recheck K+ and electrolye levels often.
- Hemodialysis for persistent hyperkalemia.
- Emergency cardiac pacing if severe hyperkalemia is causing arrhythmia’s.
- If you are aware preoperatively that your patient is hperkalemic, during CPB you can scavenge the initial flush of cardioplegia to the cell saver.
*Note: All of the above listed procedures are contingent upon approval with both the surgeon and anesthesia.
HOW TREATMENT OF HYPERKALEMIA IS ACHIEVED
NaHcO3: Correction of acidosis by diminishing the extracellular hydrogen burden and transfer of K+ intracellularly, provides intracellular binding sites for K+ in the form of potassium carbonate, buffers dextrose; corrects acidosis from shift of H+ from intracellular to extracellular.
Hypertonic saline: Correct hyponatremia; counteracts cardiotoxicity; expands extracellular compartment and dilutes K+.
Glucose and insulin: Directly promotes the movement of K+ from extracellular to intracellular compartments.
Calcium: Activates receptor sites of potassium pumps on cell membranes; replaces serum Ca, which is driven intracellularly by administration of insulin.